1. Field of the Invention
The present invention relates to the staging of a workpiece, and more particularly to staging improvements in an apparatus for tinning electronic components.
2. Description of the Related Art
The tinning of electronic components comprises the step of applying a hot solder coating to metallic leads or contact points of the component package. This tinning of a component prior to its placement on a circuit board is known in the art and is considered necessary to providing reliable, high quality solder connections. In the normal manufacturing cycle, a component may be stored for a time before utilization. During this storage time, leads can become oxidized or otherwise subject to deleterious conditions, such that when the component is later placed on and soldered to a circuit board (normally through an automated soldering system), an oxidized lead may not solder properly, leading to a board fault or defect. Accordingly, many manufacturers have found it advisable to solder coat component leads prior to use, such that when the component is later placed on the printed circuit board, the solder "reflows" and a good solder connection is assured.
Different types of systems have been used for component tinning, such as described in U.S. Pat. Nos. 4,654,227 and 4,799,450, both by inventor Cornellier and assigned to Corfin Technologies, Inc. of Chambly, Canada (hereinafter referred to as "Corfin").
One particular problem encountered with such systems relates to surface mounted components, which generally have small, closely spaced leads and low package profiles. Typical of such surface mount components are those known as LCCs (leadless chip carriers) or PLCCs (plastic leaded chip carriers). These components frequently have leads extending from all four sides of a small rectangular body, thus creating problems for mechanical staging and grasping of the component.
For example, Corfin offers a PLCC Lead Tinning System (model DTS-330LL) having staging and grasping means not disclosed by the above cited patents, illustrated in FIG. 1. A component 10 slides onto staging platform 11 from location 9 and is stopped by restraint 12. When optical detector 13 senses component 10, restraint 12 is pulled back by cylinder 14 in the direction shown. Gripper 15, on a continuously moving conveyer belt, closes as it passes over component 10, picking it up.
This configuration has some difficulties. For example, when component 10 strikes restraint 12, it tends to bounce off of staging platform 11. Restraint 16 helps this somewhat, being extended by cylinder 17 during staging, and withdrawn during pickup. Also, when restraint 12 is withdrawn in anticipation of pickup, friction between it and component 10 tends to rotate component 10, horizontally misaligning it for subsequent pickup. Further, if staging platform 11 does not receive component 10, restraint 12 remains extended in case a component is about to be received, interfering with the overhead path of gripper 15. To compensate, gripper 15 must be adjusted high enough to not strike extended restraint 12, yet low enough to successfully grasp component 10. The result is inconsistent alignment and grasping of component 10, causing gripper 15 to drop component 10, and sometimes no pickup at all.
Precise staging of components is imperative to insure that the components are properly picked up and carried through the wave soldering process.
It is an object of the present invention to provide precise and consistent staging and grasping of an electronic component in automated tinning systems such as described above.